The Hills Council and specialist crews have spent the morning cleaning up what is believed to be an illegal dumping of asbestos at North Rocks.
They responded after receiving a report of building materials found strewn along Loyalty Road.
Crews wearing special suits bagged what they could and watered down the roadway to prevent any perceived asbestos particles from escaping into the air.
They will continue to work on cleaning up the area until it is considered safe.
Council is investigating the incident.